attributes

, architecture

, availability

, CSI

, stability

, MT-Level

, standard

- attributes of interfaces

Description

The ATTRIBUTES section of a manual page contains a table defining attribute
types and their corresponding values. The following is an example of an
attributes table. Not all attribute types are appropriate for all types of
interfaces.

Architecture

Architecture defines processor or specific hardware. See -p option of uname(1). In
some cases, it may indicate required adapters or peripherals.

Availability

This refers to the software package which contains the command or
component being described on the man page. To be able to use
the command, the indicated package must have been installed. For information on
how to add a package see pkgadd(1M).

Code Set Independence (CSI)

OS utilities and libraries free of dependencies on the properties of any
code sets are said to have Code Set Independence (CSI). They have
the attribute of being CSI enabled. This is in contrast to many
commands and utilities, for example, that work only with Extended Unix Codesets (EUC),
an encoding method that allows concurrent support for up to four code
sets and is commonly used to represent Asian character sets.

For practical reasons, however, this independence is not absolute. Certain assumptions are
still applied to the current CSI implementation:

File code is a superset of ASCII.

To support multi-byte characters and null-terminated UNIX file names, the NULL and / (slash) characters cannot be part of any multi-byte characters.

Only “stateless” file code encodings are supported. Stateless encoding avoids shift, locking shift, designation, invocation, and so forth, although single shift is not excluded.

Process code (wchar_t values) is implementation dependent and can change over time or between implementations or between locales.

Not every object can have names composed of arbitrary characters. The names of the following objects must be composed of ASCII characters:

User names, group name, and passwords

System name

Names of printers and special devices

Names of terminals (/dev/tty*)

Process ID numbers

Message queues, semaphores, and shared memory labels.

The following may be composed of ISO Latin-1 or EUC characters:

File names

Directory names

Command names

Shell variables and environmental variable names

Mount points for file systems

NIS key names and domain names

The names of NFS shared files should be composed of ASCII characters. Although files and directories may have names and contents composed of characters from non-ASCII code sets, using only the ASCII codeset allows NFS mounting across any machine, regardless of localization. For the commands and utilities that are CSI enabled, all can handle single-byte and multi-byte locales released in 2.6. For applications to get full support of internationalization services, dynamic binding has to be applied. Statically bound programs will only get support for C and POSIX locales.

Interface Stability

Sun often provides developers with early access to new technologies, which allows
developers to evaluate with them as soon as possible. Unfortunately, new technologies
are prone to changes and standardization often results in interface incompatibility from
previous versions.

To make reasonable risk assessments, developers need to know how likely an
interface is to change in future releases. To aid developers in making
these assessments, interface stability information is included on some manual pages
for commands, entry-points, and file formats.

The more stable interfaces can safely be used by nearly all applications,
because Sun will endeavor to ensure that these continue to work in
future minor releases. Applications that depend only on Committed interfaces should reliably
continue to function correctly on future minor releases (but not necessarily on earlier
major releases).

The less stable interfaces allow experimentation and prototyping, but should be used
only with the understanding that they might change incompatibly or even be
dropped or replaced with alternatives in future minor releases.

“Interfaces” that Sun does not document (for example, most kernel data structures
and some symbols in system header files) may be implementation artifacts. Such
internal interfaces are not only subject to incompatible change or removal, but
we are unlikely to mention such a change in release notes.

Release Levels

Products are given release levels, as well as names, to aid compatibility
discussions. Each release level may also include changes suitable for lower levels.

Release

Version

Significance

Major

x.0

Likely
to contain major feature additions; adhere to different, possibly incompatible standard
revisions; and though unlikely, could change, drop, or replace Committed interfaces. Initial
product releases are usually 1.0.

Minor

x.y

Compared to an x.0 or earlier release (y!=0),
it is likely to contain: feature additions, compatible changes to Committed interfaces,
or likely incompatible changes to Uncommitted or Volatile interfaces.

Micro

x.y.z

Intended to be interface
compatible with the previous release (z!=0), but likely to add bug fixes,
performance enhancements, and support for additional hardware. Incompatible changes to Volatile interfaces
are possible.

In the context of interface stability, update releases (occasionally referred to as
patch releases) should be considered equivalent to Micro Releases.

Classifications

The following table summarizes how stability level classifications relate to release
level. The first column lists the Stability Level. The second column lists
the Release Level for Incompatible Changes, and the third column lists other
comments. For a complete discussion of individual classifications, see the appropriate subsection below.

Stability

Release

Comments

Committed

Major
(x.0)

Incompatibilities are exceptional.

Uncommitted

Minor (x.y)

Incompatibilities are common.

Volatile

Micro (x.y.z)

Incompatibilities are common.

The interface stability level classifications described on this manual page apply to
both source and binary interfaces unless otherwise stated. All stability level
classifications are public, with the exception of the Private classification. The precise
stability level of a public interface (one that is documented in the manual
pages) is unspecified unless explicitly stated. The stability level of an undocumented
interface is implicitly Private.

The existence of documentation other than the documentation that is a component
of the Solaris product should not be construed to imply any level
of stability for interfaces provided by the Solaris product. The only source
of stability level information is Solaris manual pages.

Committed

The intention of a Committed interface is to enable third parties to develop applications to these interfaces, release them, and have confidence that they will run on all releases of the product after the one in which the interface was introduced, and within the same Major release. Even at a Major release, incompatible changes are expected to be rare, and to have strong justifications.

Interfaces defined and controlled as industry standards are most often treated as Committed interfaces. In this case, the controlling body and/or public, versioned document is typically noted in a “Standard” entry in the Attributes table or elsewhere in the documentation.

Although a truly exceptional event, incompatible changes are possible in any release if the associated defect is serious enough as outlined in the Exceptions section of this document or in a Minor release by following the End of Feature process. If support of a Committed interface must be discontinued, Sun will attempt to provide notification and the stability level will be marked Obsolete.

Uncommitted

No commitment is made about either source or binary compatibility of these interfaces from one Minor release to the next. Even the drastic incompatible change of removal of the interface in a Minor release is possible. Uncommitted interfaces are generally not appropriate for use by release-independent products.

Incompatible changes to the interface are intended to be motivated by true improvement to the interface which may include ease of use considerations. The general expectation should be that Uncommitted interfaces are not likely to change incompatibly and if such changes occur they will be small in impact and may often have a mitigation plan.

Uncommitted interfaces generally fall into one of the following subcategorizes:

Interfaces that are experimental or transitional. They are typically used to give outside developers early access to new or rapidly changing technology, or to provide an interim solution to a problem where a more general solution is anticipated.

Interfaces whose specification is controlled by an outside body yet Sun expects to make a reasonable effort to maintain compatibility with previous releases until the next Minor release at which time Sun expects to synchronize with the external specification.

For Uncommitted interfaces, Sun makes no claims about either source or binary compatibility from one minor release to another. Applications developed based on these interfaces may not work in future minor releases.

Volatile

Volatile interfaces can change at any time and for any reason.

The Volatile interface stability level allows Sun products to quickly track a fluid, rapidly evolving specification. In many cases, this is preferred to providing additional stability to the interface, as it may better meet the expectations of the consumer.

The most common application of this taxonomy level is to interfaces that are controlled by a body other than Sun, but unlike specifications controlled by standards bodies or Free or Open Source Software (FOSS) communities which value interface compatibility, it can not be asserted that an incompatible change to the interface specification would be exceedingly rare. It may also be applied to FOSS controlled software where it is deemed more important to track the community with minimal latency than to provide stability to our customers.

It also common to apply the Volatile classification level to interfaces in the process of being defined by trusted or widely accepted organization. These are generically referred to as draft standards. An “IETF Internet draft” is a well understood example of a specification under development.

Volatile can also be applied to experimental interfaces.

No assertion is made regarding either source or binary compatibility of Volatile interfaces between any two releases, including patches. Applications containing these interfaces might fail to function properly in any future release.

Not-an-Interface

The situation occasionally occurs where there exists an entity that could be inferred to be an interface, but actually is not. Common examples are output from CLIs intended only for human consumption and the exact layout of a GUI.

This classification is a convenience term to be used to clarify such situations where such confusion is identified as likely. Failure to apply this term to an entity is not an indication that the entity is some form of interface. It only indicates that the potential for confusion was not identified.

Private

A Private interface is an interface provided by a component (or product) intended only for the use of that component. A Private interface might still be visible to or accessible by other components. Because the use of interfaces private to another component carries great stability risks, such use is explicitly not supported. Components not supplied by Sun Microsystems should not use Private interfaces.

Most Private interfaces are not documented. It is an exceptional case when a Private interface is documented. Reasons for documenting a Private interface include, but are not limited to, the intention that the interface might be reclassified to one of the public stability level classifications in the future or the fact that the interface is inordinately visible.

Obsolete

Obsolete is a modifier that can appear in conjunction with the above classification levels. The Obsolete modifier indicates an interface that is “deprecated” and/or no longer advised for general use. An existing interface may be downgraded from some other status (such as Committed or Uncommitted) by the application of the Obsolete modifier to encourage customers to migrate from that interface before it may be removed (or incompatibly changed).

An Obsolete interface is supported in the current release, but is scheduled to be removed in a future (minor) release. When support of an interface is to be discontinued, Sun will attempt to provide notification before discontinuing support. Use of an Obsolete interface may produce warning messages.

Exceptions

There are rare instances when it is in the best interest of
both Sun and the customer to break the interface stability commitment. The
following list contains the common, known reasons for the interface provider to
violate an interface stability commitment, but does not preclude others.

Security holes where the vulnerability is inherent in the interface.

Data corruption where the vulnerability is inherent in the interface.

Standards violations uncovered by a change in interpretation or enhancement of conformance tests.

An interface specification which isn't controlled by Sun has been changed incompatibly and the vast majority of interface consumers expect the newer interface.

Not making the incompatible change would be incomprehensible to our customers. One example of this would to have not incompatibly changed pcfs when the DOS 8.3 naming restrictions were abandoned.

Incompatible changes allowed by exception will always be delivered in the “most
major” release vehicle possible. However, often the consequences of the vulnerabilities
or contractual branding requirements will force delivery in a patch.

Compatibility with Earlier Interface Classification Schemes

In releases up to and including Solaris 10, a different interface classification
scheme was used. The following table summarizes the mapping between the old
and new classification schemes.

Old

New

Comments

Standard

Committed

An entry in the attributes table for the Standard
attribute type should appear.

Stable

Committed

Name change.

Evolving

Uncommitted

Actual commitments match.

Unstable

Uncommitted

Name change.

External

Volatile

Name change with expansion of
allowed usage.

Obsolete

(Obsolete)

Was a classification, now a modifier.

The increased importance of Free or Open Source Software motivated the name
change from Stable/Unstable to Committed/Uncommitted. Stable conflicted with the common use of
the term in FOSS communities.

Ambiguity in the definition of Evolving was causing difficulty in interpretation. As
part of the migration to the new classification scheme, many formerly Evolving
interfaces were upgraded to Committed. However, upon encountering the term Evolving, Uncommitted
should be inferred.

MT-Level

Libraries are classified into categories that define their ability to support multiple
threads. Manual pages containing functions that are of multiple or differing levels
describe this in their NOTES or USAGE section.

Safe

Safe is an attribute of code that can be called from a multithreaded application. The effect of calling into a Safe interface or a safe code segment is that the results are valid even when called by multiple threads. Often overlooked is the fact that the result of this Safe interface or safe code segment can have global consequences that affect all threads. For example, the action of opening or closing a file from one thread is visible by all the threads within a process. A multithreaded application has the responsibility for using these interfaces in a safe manner, which is different from whether or not the interface is Safe. For example, a multithreaded application that closes a file that is still in use by other threads within the application is not using the close(2) interface safely.

Unsafe

An Unsafe library contains global and static data that is not protected. It is not safe to use unless the application arranges for only one thread at time to execute within the library. Unsafe libraries might contain functions that are Safe; however, most of the library's functions are unsafe to call. Some functions that are Unsafe have reentrant counterparts that are MT-Safe. Reentrant functions are designated by the _r suffix appended to the function name.

MT-Safe

An MT-Safe library is fully prepared for multithreaded access. It protects its global and static data with locks, and can provide a reasonable amount of concurrency. A library can be safe to use, but not MT-Safe. For example, surrounding an entire library with a monitor makes the library Safe, but it supports no concurrency so it is not considered MT-Safe. An MT-Safe library must permit a reasonable amount of concurrency. (This definition's purpose is to give precision to what is meant when a library is described as Safe. The definition of a Safe library does not specify if the library supports concurrency. The MT-Safe definition makes it clear that the library is Safe, and supports some concurrency. This clarifies the Safe definition, which can mean anything from being single threaded to being any degree of multithreaded.)

Async-Signal-Safe

Async-Signal-Safe refers to particular library functions that can be safely called from a signal handler. A thread that is executing an Async-Signal-Safe function will not deadlock with itself if interrupted by a signal. Signals are only a problem for MT-Safe functions that acquire locks.

Async-Signal-Safe functions are also MT-Safe. Signals are disabled when locks are acquired in Async-Signal-Safe functions. These signals prevent a signal handler that might acquire the same lock from being called.

MT-Safe with Exceptions

See the NOTES or USAGE sections of these pages for a description of the exceptions.

Safe with Exceptions

See the NOTES or USAGE sections of these pages for a description of the exceptions.

Fork-Safe

The fork(2) function replicates only the calling thread in the child process. The fork1(2) function exists for compatibility with the past and is synonymous with fork(). If a thread other than the one performing the fork holds a lock when fork() is called, the lock will still be held in the child process but there will be no lock owner since the owning thread was not replicated. A child calling a function that attempts to acquire the lock will deadlock itself.

When fork() is called, a Fork-Safe library arranges to have all of its internal locks held only by the thread performing the fork. This is usually accomplished with pthread_atfork(3C), which is called when the library is initialized.

The forkall(2) function provides the capability for the rare case when a process needs to replicate all of its threads when performing a fork. No pthread_atfork() actions are performed when forkall() is called. There are dangers associated with calling forkall(). If some threads in a process are performing I/O operations when another thread calls forkall(), they will continue performing the same I/O operations in both the parent and child processes, possibly causing data corruption. For this and other race-condition reasons, the use of forkall() is discouraged.

In all Solaris releases prior to Solaris 10, the behavior of fork() depended on whether or not the application was linked with -lpthread (POSIX threads, see standards(5)). If linked with -lpthread, fork() behaved like fork1(); otherwise it behaved like forkall(). To avoid any confusion concerning the behavior of fork(), applications can specifically call fork1() or forkall() as appropriate.

Cancel-Safety

If a multithreaded application uses pthread_cancel(3C) to cancel (that is, kill) a thread, it is possible that the target thread is killed while holding a resource, such as a lock or allocated memory. If the thread has not installed the appropriate cancellation cleanup handlers to release the resources appropriately (see pthread_cancel(3C)), the application is “cancel-unsafe”, that is, it is not safe with respect to cancellation. This unsafety could result in deadlocks due to locks not released by a thread that gets cancelled, or resource leaks; for example, memory not being freed on thread cancellation. All applications that use pthread_cancel(3C) should ensure that they operate in a Cancel-Safe environment. Libraries that have cancellation points and which acquire resources such as locks or allocate memory dynamically, also contribute to the cancel-unsafety of applications that are linked with these libraries. This introduces another level of safety for libraries in a multithreaded program: Cancel-Safety. There are two sub-categories of Cancel-Safety: Deferred-Cancel-Safety, and Asynchronous-Cancel-Safety. An application is considered to be Deferred-Cancel-Safe when it is Cancel-Safe for threads whose cancellation type is PTHREAD_CANCEL_DEFERRED. An application is considered to be Asynchronous-Cancel-Safe when it is Cancel-Safe for threads whose cancellation type is PTHREAD_CANCEL_ASYNCHRONOUS. Deferred-Cancel-Safety is easier to achieve than Asynchronous-Cancel-Safety, since a thread with the deferred cancellation type can be cancelled only at well-defined cancellation points, whereas a thread with the asynchronous cancellation type can be cancelled anywhere. Since all threads are created by default to have the deferred cancellation type, it might never be necessary to worry about asynchronous cancel safety. Most applications and libraries are expected to always be Asynchronous-Cancel-Unsafe. An application which is Asynchronous-Cancel-Safe is also, by definition, Deferred-Cancel-Safe.

Standard

Many interfaces are defined and controlled as industry standards. When this is
the case, the controlling body and/or public, versioned document is noted in
this section.

Programmers producing portable applications should rely on the interface descriptions present in
the standard or specification to which the application is intended to conform,
rather than the manual page descriptions of interfaces based upon a public
standard. When the standard or specification allows alternative implementation choices, the manual page
usually only describes the alternative implemented by Sun. The manual page also
describes any compatible extensions to the base definition of Standard interfaces provided
by Sun.

No endorsement of the referenced controlling body or document should be inferred
by its presence as a “Standard” entry. The controlling body may be
a very formal organization, as in ISO or ANSII, a less formal,
but generally accepted organization such as IETF, or as informal as the sole
contributor in the case of FOSS (Free or Open Source Software).